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diodes

joe becraft

Oct 26, 2015
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question... I have a pickup truck, I am wanting to wire up work lights on the back bumper, tying them in to the reverse lights as well as the cargo light... i know if I run a wire connecting the new work light/reverse lights to the cargo light, they will all come on together, the thing is, when the cargo light comes on, so does the dome light inside the cab...

my question is, can I put a diode inline between the cargo light and the dome light so basically when the dome light is on the cargo light is, but if the cargo light is on, the dome light isn't... do I need resistors or anything else, or will just a diode work?

thanks!
Joe
 

Martaine2005

May 12, 2015
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Answer...A relay will probably be needed to the work lights on the bumper!!
Question.. What are cargo lights? I know a dome light..

Martin
 

joe becraft

Oct 26, 2015
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a cargo light is the light on the back of the cab above the window on either side of the high mount break night... I have hooked my work lights up on the bumper to the reverse lights and they work fine...

can a diode be used alone on any operation, not jus what I am talking about...?
 

bigone5500

Apr 9, 2014
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I would think you will need to make sure your wiring is large enough to handle the extra current.

Why not just run a new wire from the battery and install a toggle switch inside the cab? You can use small guage wire to operate a relay and not have to worry with running large guage wire inside the cab.

Also, can you post a link to the work lights you are using?
 

Bluejets

Oct 5, 2014
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Easy to get "feedback" in auto circuits, mostly due to the fact the wiring is mostly earth return switching.
 

bigone5500

Apr 9, 2014
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As an alternative, you could switch the relay with the key switch acc. mode.

As a side note, you only have to run one wire to the relay from the toggle switch. Jump off the positive wire from the battery and go to one terminal of the relay coil. Then run a wire from the other coil terminal and go to the toggle switch. Ground the other terminal of the switch and it will work.

Someone please correct me if I am wrong about this. But I'm thinking that there should be a diode across the coil. The voltage drop from the work light shouldn't be too much that it would cause the relay to drop out. I used an LED as the work light as Fritzing does not have an incandescent bulb part. You can use an SPST toggle alternatively.

Work Light Schematic Example.jpg
 
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Martaine2005

May 12, 2015
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I think the bottom line is a relay for any aux lighting.
It may work very well, but were the supply wires getting hot or warm?.
Best to do a proper install and do it properly! A couple of hours work and you know it is final.
BTW, you can put diode steering in place provided you use the correct specs for the diodes.
But a better way would be to change/alter the connections on the dome/cargo switch.

Martin
 

davenn

Moderator
Sep 5, 2009
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Someone please correct me if I am wrong about this. But I'm thinking that there should be a diode across the coil.

generally, yes, specially when the relay is being switched by IC's, transistors, but in this example, not really an issue


Dave
 

thaers3d

Nov 7, 2015
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you can use the diode alone but you must use suitable one with heat sink .
 
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